The present invention relates to light beam scanning devices using an oscillation type optical deflector. More particularly, the invention relates to a light beam scanning device which reciprocally scans a light beam in a parallel pattern.
Devices such as a rotary multi-surface mirrors, deflectors utilizing an acousto-optical effect, and galvanometer mirrors are currently in extensive use for deflecting laser beams. Among these devices, the galvanometer mirror is especially advantageous in that it is small in size, low in manufacturing cost, and simple in operation. However, techniques for scanning a light beam in a reciprocating manner using an oscillation type optical deflector such as a galvanometer mirror are disadvantageous in the following points. As shown in FIG. 1, a light beam 2 from a laser light source 1 is modulated by an optical modulator 3 and the light beam 2 thus modulated is scanned over a scanned surface such as a recording medium 5 by the reciprocal oscillation motion in the direction A of a galvanometer mirror 4. This is the main scanning operation. An auxiliary scanning operation is effected by moving the recording medium 5 in the direction B at a constant speed. In this case, recorded scanning lines 6.sub.1 and 6.sub.2 are not parallel to one another and therefore the recorded picture is very low in quality.
If only one of the "go" and "return" directions of the reciprocal oscillation motion is employed for the light scanning, then the resultant scanning lines are parallel to one another and the distance between adjacent scanning lines is constant. However, this method is still disadvantageous in that its scanning speed is low.
Accordingly, an object of this invention is to provide a reciprocating scanning type light beam scanning device in which the above-described difficulties have been eliminated.